In general, inkjet printing machines or printers include at least one printhead that ejects drops of liquid ink onto a recording or image forming medium. A phase-change inkjet printer employs phase change inks that are solid at ambient temperature, but transition to a liquid phase at an elevated temperature. The melted ink can then be ejected from a printhead to form an ink image on an image receiving member. The ink image may be formed on a layer of release agent coating an intermediate imaging member, such as a rotating drum or belt, and then transferred to an image receiving substrate, such as a sheet of paper, as the substrate passes through a nip formed between a transfix roller and the intermediate imaging member. In other printing systems, the ink can be ejected directly onto printing media directed past the printheads.
Printers typically conduct various maintenance operations to ensure proper operation of the inkjets in each printhead. One known maintenance operation removes particles or other contaminants within a printhead by urging ink through some or all of the inkjets in the printhead. This purged ink flows from the apertures of the inkjets that are located in a faceplate of each printhead onto the faceplate. The ink rolls downwardly under the effect of gravity to an ink drip bib mounted at the lower edge of the faceplate or onto a flexure chute mounted on a maintenance station. The drip bib or flexure chute is configured to collect the liquid ink and direct the ink into an ink receptacle. In some printers, one or more wipers are manipulated to contact the faceplate of each printhead and wipe the purged ink toward the drip bib to facilitate the collection and removal of the purged ink. Alternatively, in systems where the printhead faces downwardly, some of the ink from a purge remains on the surface of the faceplate due to ink surface tension. This remaining ink can also be removed with a wiper passing across the faceplate.
Inkjet printheads are typically coated with a hydrophobic material, for example polytetrafluoroethylene, to maintain a low surface energy on the printhead face to enable ink on a printhead to run off the printhead face, but also to keep the ink held within the apertures from leaking, flowing, or drooling onto the surface of the printhead face. However, over time the hydrophobic coating on the printheads can wear off and the surface energy of the printhead face increases. The increased surface energy can result in ink adhering to the printhead faceplate near the apertures during printing or after purging, which can result in interference with subsequent jetting from the apertures. Typically, the ink in the printhead is held at a negative static pressure (as measured at the apertures) to disable the ink from flowing onto the faceplate. In addition, the low surface energy of the faceplate surface helps prevent the ink in the apertures from flowing or drooling out of the head and onto the faceplate surface, where the presence of the ink can interfere with jetting performance. Thus, increased surface energy of the faceplate surface reduces the ability of the apertures to retain ink, increases ink drooling, and increases the need for the negative static pressure within the apertures. This increase in pressure can reduce the performance latitude of the printhead.
In some printers, a surface treatment fluid is applied to the face of the printhead to reduce the surface energy of the printhead faceplate. Surface treatment fluid is typically applied by manually wiping the printhead face with an applicator bearing a surface treatment fluid. Manual application of surface treatment fluid, however, often leaves a non-uniform layer and amount of surface treatment fluid, and may inadvertently damage the printhead face. Additionally, loss of productivity occurs while the printer is off line to apply the treatment fluid. Improved surface treatment of printheads is therefore desirable.